High aspect ratio etch using modulation of RF powers of various frequencies

ABSTRACT

A method for etching a high aspect ratio feature through a mask into a layer to be etched over a substrate is provided. The substrate is placed in a process chamber, which is able to provide RF power at a first frequency, a second frequency different than the first frequency, and a third frequency different than the first and second frequency. An etchant gas is provided to the process chamber. A first etch step is provided, where the first frequency, the second frequency, and the third frequency are at power settings for the first etch step. A second etch step is provided, where the first frequency, the second frequency, and the third frequency are at a different power setting.

RELATED APPLICATIONS

This application is a divisional of prior U.S. patent application Ser.No. 10/737,022, entitled “High Aspect Ratio Etch Using Modulation of RFPowers of Various Frequencies”, filed on Dec. 15, 2003 now U.S. Pat. No.7,144,521 by inventors Camelia Rusu et al., which is acontinuation-in-part of U.S. patent application Ser. No. 10/645,665entitled “Multiple Frequency Plasma Etch Reactor” by Raj Dhindsa et al.,filed Aug. 22, 2003 now U.S. Pat. No. 7,405,521 all of which isincorporated herein by reference and from which priority under 35 U.S.C.§120 is claimed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for etching features, such as highaspect ratio features, into an etch layer.

2. Description of the Related Art

The present invention relates to the formation of semiconductor devices.

It is known to apply plasma excitation fields at two differentfrequencies to a region of a vacuum chamber for plasma processing aworkpiece, wherein the region is coupled to a gas that the fieldsconvert into the processing plasma. The workpiece is usually asemiconductor wafer, or dielectric plate and the plasma is involved informing integrated circuit features on the workpiece. Typically, theplasma excitation fields at the two different frequencies are suppliedto the region by a pair of spaced electrodes in the chamber or oneelectrode in the chamber and a reactance, in the form of a coil, locatedoutside the chamber. The excited plasma typically dry etches theworkpiece, but in some instances results in materials being deposited onthe workpiece. High frequency RF power (having a frequency in excess ofapproximately 10 MHz) typically controls the density of the plasma,i.e., the plasma flux, while RF power having a low to medium frequency(in the range of 100 kHz to approximately 10 MHz) typically controls theenergy of ions in the plasma and incident on the workpiece.

As the size of the features continues to decrease, there are increasedrequirements for precise control of various parameters of the plasmaprocessing a workpiece. Amongst the plasma parameters requiring precisecontrol are the plasma chemistry (i.e., types of ionic and radicalspecies), the plasma flux and the ion energy of the plasma incident onthe substrate. With the shrinking feature sizes and use of new materialsin fabrication of integrated circuits, windows involved in processingthe workpiece are decreasing in size, while pushing the limits onpresently available plasma processors, particularly processors foretching. The shrinking feature sizes and requirements for new materialslimit the use of the same reactor, i.e., vacuum processing chamber, fordifferent etch applications.

High-aspect ratio (HAR) openings have a high opening depth to openingdiameter ratio. A mask, such as a photoresist mask or a hard mask, isused to provide an opening pattern. In the specification and claims, ahigh aspect ratio feature is defined as a feature with a depth todiameter ratio greater than 10:1.

As the integrated circuit dimensions shrinks, the CDs and profilecontrol along with the etch stop in high aspect ratio contact holeetching becomes very challenging problem in dielectric etch. The variousfeatures (top and bottom CD, profile angle, bowing and necking) of thecontact/via hole depend upon plasma properties (e.g. plasma chemistry,ions to neutral flux, ion energy distribution etc.) and substrateproperties (doping level of the dielectric material, temperature of thesubstrate etc.). However, for the same substrate properties, the plasmaproperties vary (the ion to neutral ratio, the total flux etc.) as thehigh aspect ratio contact etching progresses. This causes a lower etchrate as the aspect ratio of the holes increases that leads to eitheretch stop or taper profile etc. Thus, the etching conditions has to betailored to the etch depth and required profile providing an improvedetch.

SUMMARY OF THE INVENTION

To achieve the foregoing and in accordance with the purpose of thepresent invention, a method for etching a high aspect ratio featurethrough a mask into a layer to be etched over a substrate is provided.The substrate is placed in a process chamber, which is able to provideRF power at a first frequency, a second frequency different than thefirst frequency, and a third frequency different than the first andsecond frequency. An etchant gas is provided to the process chamber. Afirst etch step is provided, where the first frequency is at a firstpower level, the second frequency is at a second power level, and thethird frequency is at a third power level, where at least two of thethree powers are greater than zero, where the first etch etches afeature in the layer to be etched to a first depth. A second etch stepis provided, where the first frequency is at a fourth power level, thesecond frequency is at a fifth power level, and the third frequency isat a sixth power level, wherein at least one of the fourth and sixthpowers is greater than zero and the fifth power is greater than zero,and where a condition is selected from the group of the first power notbeing equal to the fourth power or the third power not being equal tothe sixth power, where the second etch etches the feature in the layerto be etched to a second depth greater than the first depth.

In another manifestation of the invention, an apparatus for etching afeature in an etch layer through a mask over a substrate is provided. Aplasma processing chamber comprises a chamber wall forming a plasmaprocessing chamber enclosure, a substrate support for supporting asubstrate within the plasma processing chamber enclosure, a pressureregulator for regulating the pressure in the plasma processing chamberenclosure, at least one electrode for providing power to the plasmaprocessing chamber enclosure for sustaining a plasma, a gas inlet forproviding gas into the plasma processing chamber enclosure, and a gasoutlet for exhausting gas from the plasma processing chamber enclosure.A gas source is in fluid connection with the gas inlet. A first powersource provides power within the chamber wall at a first frequency. Asecond power source provides power within the chamber wall at a secondfrequency different than the first frequency. A third power sourceprovides power within the chamber wall at a third frequency differentthan the first frequency and the second frequency. A controller iscontrollably connected to the gas inlet, the first power source, thesecond power source, and the third power source. The controllercomprises at least one processor and computer readable media, whichcomprises computer readable code for introducing an etchant gas throughthe gas inlet, computer readable code for performing a first etch stepand computer readable code for providing a second etch step. The firstetch step comprises providing energy from the first power source at afirst power level, providing energy from the second power source at asecond power level, and providing energy from the third power source ata third power level, wherein in the first power level and the thirdpower level are greater than zero, wherein the first etch is used toetch a feature in the layer to be etched to a first depth. Computerreadable code for performing a second etch step, comprises providingenergy from the first power source at a fourth power level, providingenergy from the second power source at a fifth power level, andproviding energy from the third power source at a sixth power level,wherein in the first power level and the third power level are greaterthan zero, wherein the first etch is used to etch a feature in the layerto be etched to a first depth, wherein at least one of the fourth andsixth power levels is greater than zero and the fifth power level isgreater than zero, and wherein a condition is selected from the group ofthe first power level not being equal to the fourth power level or thethird power level not being equal to the sixth power level, wherein thesecond etch etches the feature in the layer to be etched to a seconddepth greater than the first depth.

These and other features of the present invention will be described inmore details below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a partially schematic diagram of a vacuum plasma processor inaccordance with a preferred embodiment of the present invention.

FIGS. 2A-C form a block diagram of the electronic circuitry included inthe controller of FIG. 1 in combination with a schematic representationof the electric parts of the vacuum processor chamber illustrated inFIG. 1.

FIG. 3 is a partially schematic diagram of a vacuum plasma processor inaccordance with another embodiment of the present invention.

FIG. 4 is a high level flow chart of a process used in an embodiment ofthe invention.

FIGS. 5A-D are schematic cross-sectional views of a substrate with anetch layer into which a high aspect ratio feature is etched.

FIGS. 6 A-C are schematic cross-sectional views of a substrate forincreasing aspect ratio of the feature as the etch process progresses.

FIG. 7 shows the plasma speciation for the same chemistry and same powerlevels as function of RF frequency supplied.

FIGS. 8A-B are graphs of ion energy and distribution at various powersat different frequencies.

FIGS. 9A and 9B illustrate a computer system, which is suitable forimplementing a controller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

Reference is now made to FIG. 1 of the drawing wherein plasma processorvacuum chamber 10, having longitudinal axis (i.e., centerline) 11 isillustrated as including electrically conductive metal wall 12, bottomelectrode assembly 13 and top electrode assembly 14. Wall 12 has acircular inner periphery, coaxial with axis 11. Wall 12 is grounded,i.e., at DC and RF reference potentials. Vacuum pump 9 maintains theinterior of chamber 10 at a vacuum on the order of 0.001 to 500 torrduring processing. The interior of chamber 10 includes confined plasmaregion 8 between a bottom boundary close to the top face of bottomelectrode assembly 13 and a top boundary close to the bottom face of topelectrode assembly 14; the side boundary of confined plasma region 8 isspaced from wall 12.

Bottom electrode assembly 13, frequently referred to as a bottomelectrode, is coaxial with axis 11 and is secured to electric insulatingring 17, which in turn is secured to metal, grounded base 19 of chamber10. Electrode assembly 13 includes circular, central metal electrode 16that is coaxial with axis 11 and has an upper surface for receiving acircular workpiece 18, typically a semiconductor wafer having a diametersubstantially equal to the diameter of metal electrode 16. Whenworkpiece 18 is properly in place, its center is coincident with axis11. Electrode 16 can be connected to a DC chucking voltage source (notshown) for clamping workpiece 18 to electrode 16 using electrostaticforces. The temperature of electrode 16 and workpiece 18 are controlledin a manner known to those skilled in the art by connecting heliumsource 20 to a region (not shown) in electrode 16 by way of conduit 21and valve 22, responsive to an electric signal that controller 24derives in response to (1) a temperature set point supplied to thecontroller by set point source 25 and (2) a measure of the temperaturein the electrode, as indicated by a signal derived by temperaturemonitor 26 embedded in electrode 16.

Bottom electrode assembly 13 also includes electric insulator ring 28,typically made of quartz. Ring 28 is secured to the top face ofinsulator ring 17, is coaxial with axis 11 and has an inner diametersubstantially equal to the diameter of workpiece 18 so that theperiphery of workpiece 18, when the workpiece is properly in place,almost abuts the inner periphery of ring 28. The portion of the top faceof ring 17 outside ring 28 and the side wall of ring 17 are covered byinsulator ring 33 and grounded metal ring 32, respectively. Insulatingring 33 is overlaid by metal electrode ring 34 that can be covered orcoated with a layer (not shown) of dielectric or conductive material.Electrically conductive ring 34 and the layer that covers or coats itare made of a material that does not contaminate the chemistry of theplasma in region 8. Such a material is a suitable relatively highconductivity semiconductor, e.g., intrinsic silicon. Alternatively, ring34 is a metal covered by a suitable non-contaminating material. Ring 34is electrically insulated from grounded metal ring 32 by dielectric,insulating ring 33 under certain circumstances and electricallyconnected to grounded ring 32 under other circumstances. Rings 33 and 34are coaxial with axis 11, and extend horizontally between the outer edgeof bottom electrode assembly 13 and ring 28.

Top electrode assembly 14 includes central electrode 36, coaxial withaxis 11 and having a bottom face 36 a made of electrically conductiveintrinsic silicon that does not contaminate the chemistry of the plasmain region 8. Electrode 36 includes internal passages (not shown) andnumerous showerhead openings (not shown), both connected in fluid flowrelation to a suitable source 37 of process gases that flow through theshowerhead openings into region 8 where the gases are converted into aplasma that processes workpiece 18. Electrode 36 includes a heatingand/or cooling arrangement 45 responsive to an electric signal thatcontroller 24 supplies to arrangement 45 via lead 35 in response to aset point signal supplied to the controller by set point source 25, aswell as a signal indicative of the temperature of electrode 36, asderived by temperature gauge 39, embedded in assembly 14.

Assembly 14 also includes insulator ring 38 and metal ring 40. Ring 38is coaxial with axis 11, preferably made of quartz and approximatelyaligned with ring 28. Ring 38 has an inner periphery abutting the outerperiphery of central electrode 36. Metal ring 40, coaxial with axis 11,has inner and outer peripheries respectively abutting the outerperiphery of insulator ring 38 and the inner periphery of side wall 12so that ring 40 is at RF and DC ground potential. The lower, inner faceof metal ring 40 is covered by electrical insulating ring 41 thatcarries an electrically conductive electrode ring 42. Electrode ring 42is either coated or covered with a layer (not shown) of conductive orinsulating material that does not contaminate the chemistry of theplasma in region 8. Ring 42 is electrically insulated from ring 40 andwall 12 by ring 41 and a downwardly depending flange (not shown) of ring41 under certain circumstances and is electrically connected to ring 40and wall 12 under other circumstances.

From the foregoing, confined plasma region 8 has a top boundarydetermined by (1) the bottom face 36 a of electrode 36, (2) the bottomface of insulator ring 38 and (3) the bottom face of electrode ring 42,and a bottom boundary determined (1) by the top face of workpiece 18(when the workpiece is in place), (2) the top face of insulator ring 28and (3) the top face of electrode ring 34. Motor 43 controls the spacingbetween the top and bottom boundaries of region 8 by moving the bottomface of top electrode assembly 14 up-and-down relative to the top faceof bottom electrode assembly 13. Motor 43 responds to a signal fromcontroller 24 to set the spacing between the faces of electrodeassemblies 13 and 14 at an experimentally determined optimum value forthe particular frequencies that excite the plasma processing ofworkpiece 18, as derived from set point source 50.

The sides of confined plasma region 8 are bounded by spaced, verticallystacked louvers 44, made of a material that does not contaminate thechemistry of the plasma in region 8. The louvers 44 are made of amaterial that is either electrically insulating (preferably adielectric, such as quartz) or somewhat electrically conductive (e.g.silicon carbide) so that the louvers are electrically powered, or floatelectrically or are electrically grounded. Louvers 44 are such that nosubstantial amount of plasma flows through the slots between louvers 44.However, un-ionized gas in region 8 escapes through the slots betweenlouvers 44 to region 46 in chamber 10 between wall 12 and ring 32 and ispumped from the interior of chamber 10 by pump 9 through suitableopenings in base 19.

Louvers 44 are fixedly spaced from each other in the vertical directionby a suitable spacing arrangement (not shown) and are driven up and downrelative to each other and to bottom assembly 13 by motor 47 to controlthe pressure in confined plasma region 8. The pressure in region 8 iscontrolled by a pressure set point that set point source 25 supplies tocontroller 24 and an output signal of pressure gauge 48 in region 8.Controller 24 responds to the pressure set point and the output signalof pressure gauge 48 to control motor 47, and thereby vary the spacingbetween the bottom face of the lowest louver 44 and the top face ofelectrode assembly 13. Consequently, the pressure in region 8 ismaintained at the pressure set point. Louvers 44 are arranged so thatthe louvers do not move in response to activation of motor 43, so thatthe pressure in confined plasma region 8 is controlled independently ofthe spacing between electrode assemblies 13 and 14.

Controller 24 responds to set point source 50 to control coupling ofvarious combinations of several different RF frequencies from sourcearrangement 51 to electrodes 16, 34, 36 and 42. The different RFfrequencies applied to electrodes 16, 34, 36 and 42 can have differentpowers and control different phenomena of the plasma in confined region8. In the embodiment of FIG. 1, controller 24 selectively applies up tothree frequencies from source arrangement 51 to electrodes 16, 34, 36and 42. Source arrangement 51 is illustrated as including three separatesources 52, 54 and 56 that can be fixed frequency sources, but arepreferably low-power, variable frequency oscillators. Alternately sourcearrangement 51 includes a single low power synthesizer that can derivethree selected frequencies. The low power sources drive associatedvariable power gain RF power amplifiers having variable frequency passbands that are varied as the frequency of the source associated with aparticular amplifier is varied. To this end, each of sources 52, 54 and56 has an associated frequency and power setting 58 and 59. Typically,the frequency of source 52 is in a relatively low range between 100 kHzand 10 MHz, the frequency of source 54 is in a midrange between 10 MHzand 150 MHz, and the frequency of source 56 is in a relatively highrange between 27 MHz and 300 MHz. In one actually tested arrangement,the frequencies of sources 52, 54 and 56 were respectively set at 2 MHz,27 MHz and 60 MHz. Various combinations of the frequencies and thepowers of the RF energy applied to region 8 affect the distribution ofthe density of plasma, the ion energy and the DC bias voltage of theplasma in confined region 8, and the chemistry of the plasma in region8.

The frequencies of sources 54 and 56 control the chemistry of the plasmabecause greater dissociation of the plasma occurs as the plasmaexcitation frequency increases, if all other significant plasmaexcitation parameters remain constant. In particular, there is anincrease in the percentage of lighter etchant molecules in the plasma asfrequency increases. The high frequencies applied to the plasma resultin greater molecular fragmentation.

Driving electrodes 16, 34, 36 and 42 with various combinations offrequencies and powers from sources 52, 54 and 56 enables the plasma tobe tailored for various purposes, e.g., to provide uniform ornon-uniform plasma density, ion energy and molecular fragmentation.

Controller 24 responds to output signals from set point source 50 andthe RF outputs of source arrangement 51 to control the application ofseveral frequencies from source arrangement 51 to electrodes 16, 34, 36and 42 in various combinations and permutations. In a particularembodiment, set point source 50 activates controller 24 so (1) at leastone of the frequencies, but up to all three frequencies, from sources52, 54 and 56 drive electrode 16 while electrodes 34, 36, and 42 aregrounded; (2) at least two of the frequencies from sources 52, source 54and 56 drive electrodes 16 and 36 while electrodes 34 and 42 aregrounded; (3) only one of sources 54 or 56 drives either electrode 16 or36 or only source 52 drives electrode 16, while electrodes 34 and 42 aregrounded; (4) electrode 34 is driven by source 52 and/or source 54 or isconnected to ground via a filter having a pass band for the frequency ofsource 52 and/or source 54 (i.e., frequencies F2 and F3) while theremaining electrodes 16, 36, and 42 have various connections to sources52, 54, and 56; and (5) electrode 42 is driven by source 52 and/orsource 54 or is connected to ground via a filter having a pass band forthe frequency of source 52 and/or source 54 (i.e., frequencies F2 andF3) while the remaining electrodes 16, 34, and 36 have variousconnections to sources 52, 54, and 56.

Reference is now made to FIG. 2 of the drawing, a block diagramincluding the circuitry of controller 24 for selectively coupling theoutput of sources 52, 54 and 56 to electrodes 16, 34, 36 and 42.

Low frequency source 52, having a frequency F1, drives only centerelectrode 16 of bottom electrode assembly 13. To this end, the output ofsource 52 is coupled to match/tunable ground network 58 via voltage,current and phase angle sensor 60, as well as switches 62 and 64.Network 58 includes variable reactances having values that are preset toprovide approximate matching between the output impedance of source 52and the expected impedance of the plasma in region 8 for the frequencyof source 52. Sensor 60 derives output signals indicative of the currentflowing between source 52 and match/tunable ground network 58, thevoltage between the output of source 52 and ground 58 and the phaseangle between the sensed voltage and current. Sensor 60 supplies thesecurrent, voltage and phase angle signals to controller 66, whichresponds to them to control the frequency of source 52 to maintain asubstantially precise impedance match between the output impedance ofsource 52 and the impedance of the plasma at the frequency of source 52in a manner known to those skilled in the art. Additionally, if thefrequency of source 52 is fixed, sensor 60 supplies these current,voltage and phase angle signals which responds to them to control thevariable reactances of matching network 58 to maintain a substantiallyprecise impendence match between the output impedance of source 52 andthe impendence of the plasma at the frequency of source 52 in a mannerknown to those skilled in the art. The variable reactances of network58, when matched, are approximately tuned to the frequency of source 52to provide a low impedance path for the frequency of source 52 in bothdirections and a high impedance path for the frequencies of sources 54and 56 so that the frequencies of sources 54 and 56 are substantiallyattenuated, i.e., rejected by network 58. As the frequency of source 52changes in response to set point changes thereof by an operator,controller 66 correspondingly varies the reactances of network 58 tomaintain the low impedance path for the frequency of source 52 andapproximate matching between the source output impedance and theimpedance of the plasma for the frequency of source 52.

It is usually desirable when source 52 drives electrodes 16 for electricfields at the frequency of source 52 to subsist between electrodes 16and 36. To this end, electrode 36 is selectively connected to groundthrough switch 65 and bandpass filter 67, having a center frequencyequal to the nominal frequency of source 52, as set by the operator.Consequently, current at the frequency of source 52 flows from electrode36 to ground through filter 67 which has a large impedance to thefrequencies of sources 54 and 56 and therefore substantially blockscurrent at the frequencies of sources 54 and 56. Under thiscircumstance, it is frequently desirable to connect electrodes 34 and 42to DC and RF ground, a result achieved by controller 24 closing switches69 and 71, respectively connected between electrodes 34 and 42 andground. For other purposes, controller 24 grounds electrode 16 for RFand DC by closing switch 72, connected between electrode 16 and ground.

In normal operation while source 52 drives electrode 16, switches 62 and64 are connected as illustrated. However, under other circumstances,while source 52 is decoupled from electrode 16, switches 62 and 64 areactivated by controller 24 so that switches 62 and 64 respectivelyengage first terminals of resistors 68 and 70, both of which have valuesequal to the output impedance of source 52. The second terminals ofresistors 68 and 70 are connected to ground so that when source 52 isdecoupled from electrode 16, the output of source 52 drives a loadmatched to the output impedance of source 52. Under these conditions,the input terminals of network 58 are connected across resistors 70 sothe impedance from electrode 16 looking back into the output terminalsof network 58 is the same as when source 52 is coupled to electrode 16.In addition, because network 58 is tuned approximately to the frequencyof source 58, network 58 provides a low impedance at the frequency ofsource 52 from electrode 16 through the tuned circuitry of network 58 toground through resistor 70 and a high impedance at the frequency ofsources 54 and 56 from electrode 16 through the tuned circuitry ofnetwork 58 to ground through resistor 70.

Mid frequency source 54, having a frequency F2, can drive (1) onlyelectrode 16, (2) only electrode 36, (3) both electrodes 16 and 36simultaneously, (4) only electrode 34, (5) only electrode 42, (6) bothelectrodes 34 and 36 simultaneously, (7) both electrodes 34 and 42simultaneously, and (8) both electrodes 36 and 42 simultaneously.

To these ends, the output of source 54 is coupled to three positioncoaxial RF switch 74, having first and second output terminalsselectively connected to drive match/tunable ground networks 76 and 78at separate times. Networks 76 and 78 are identical to each other andsimilar to network 66, except that networks 76 and 78 provide matchingand a tunable ground for the frequency of source 54. As such, networks76 and 78 pass current and voltage at the frequency of source 54, butblock current and voltage at the frequencies of sources 52 and 56.Switch 74 includes a third terminal connected to an input port of powersplitter 80, having first and second output ports on which are derivedoppositely phased power at the frequency of source 54. The power at theoutput ports of splitter 80 can be the same or different, depending uponthe design and setting of the splitter; the setting of splitter 80 canbe set manually by the operator or automatically by controller 24 inresponse to a recipe program a memory of the controller stores. Power atthe first and second output ports of splitter 80 is respectivelysimultaneously supplied to networks 76 and 78. Power is supplied fromthe first output terminal of switch 74 or the first output terminal ofsplitter 80 to the input terminals of network 76 via voltage, currentand phase angle sensor 82, as well as switches 84 and 86, respectivelyselectively connected to ground through resistors 88 and 90. Power issupplied from the second output terminal of switch 74 or the secondoutput terminal of splitter 80 to the input terminals of network 78 viavoltage, current and phase angle sensor 92, as well as switches 94 and96, respectively connected to ground through resistors 98 and 100.Controllers 102 and 104 are respectively associated with networks 76 and78, as well as sensors 82 and 92. Controllers 102 and 104 respond to theoutputs of sensors 82 and 92 and operator inputs to control the valuesof the reactances of network 76 and 78 and the frequency of source 54 inthe same manner as described supra for controller 66.

Three position coaxial RF switch 106 responds to control signals fromcontroller 24 to selectively connect the output of network 76 toelectrode 16 or electrode 34, or open circuit the output of network 76.Three position coaxial RF switch 108 operates in conjunction with switch106 by responding to control signals from controller 24 to selectivelyconnect the output of network 78 to electrode 36 or electrode 42, oropen circuit the output of network 78. While controller 24 activatesswitch 74 to couple the output of source 54 to network 76, thecontroller activates switch 106 to connect the output of network 76 toeither electrode 16 or electrode 34. If controller 24 causes the outputof network 76 to be coupled to electrode 16 by causing switch 74 toengage the first output terminal of switch 74, the controller (1) opensswitch 72 to prevent electrode 16 from being grounded and (2) eitheropens or closes switch 69 to decouple electrode 34 from ground or toground electrode 34, respectively. If controller 24 causes the output ofnetwork 76 to be coupled to electrode 34 by causing switch 74 to engagethe first output terminal of switch 74, the controller (1) opens switch69 to prevent electrode 34 from being grounded and (2) either opens orcloses switch 72 to decouple electrode 16 from ground or to groundelectrode 16, respectively. If controller 24 causes the output ofnetwork 78 to be coupled to electrode 36 by causing switch 74 to engagethe second output terminal of switch 74, the controller (1) opens switch110 that RF and DC grounds electrode 36, when closed, and (2) eitheropens or closes switch 71 to decouple electrode 42 from ground or toground electrode 42, respectively. If controller 24 causes the output ofnetwork 78 to be coupled to electrode 42 by causing switch 74 to engagethe second output terminal of switch 74, the controller (1) opens switch71 to decouple ground from electrode 42 and (2) either opens or closesswitch 110 to decouple electrode 36 from ground or to ground electrode36, respectively. If controller 24 activates switch 74 so that splitter80 simultaneously supplies power to networks 76 and 78, controller 24activates switches 69, 71, 72 and 110 to prevent any of electrodes 16,34, 36 or 42 that are connected to the output terminals of network 76and/or 78 from being grounded.

High frequency source 56, having a frequency F3, can drive (1) onlyelectrode 16, (2) only electrode 36, (3) both electrodes 16 and 36simultaneously, (4) only electrode 34, (5) only electrode 42, (6) bothelectrodes 34 and 36 simultaneously, (7) both electrodes 34 and 42simultaneously, and (8) both electrodes 36 and 42 simultaneously.

To these ends, the output of source 56 drives circuitry that isidentical to the circuitry that source 54 drives, except that thematch/tunable ground networks 112 and 114 associated with source 56 arepreset to be tuned to the nominal frequency of source 56 so networks 112and 114 pass the current and voltage from source 56, but block thecurrent and voltage of sources 52 and 54. Thus, the output of source 56is coupled to three position coaxial RF switch 116, having first, secondand third output terminals respectively connected to drive networks 112and 114 and splitter 118, having first and second output terminalsconnected to drive input terminals of networks 112 and 114. The firstoutput terminals of switch 116 and splitter 118 are selectivelyconnected to the input terminals of matching network 112 via voltage,current and phase angle sensor 120, as well as switches 122 and 124,while the second output terminals of switch 116 and splitter 118 areselectively connected to the input terminals of matching network 114 viavoltage, current and phase angle sensor 126, as well as switches 128 and130. Switches 122, 124, 128 and 130 are respectively selectivelyconnected to ground by resistors 131-134, each of which has a valueequal to the output impedance of source 56. Controllers 136 and 138 arerespectively associated with networks 112 and 114, as well as sensors120 and 126, to control networks 112 and 114, as well as the frequencyof source 56.

Controller 24 activates (1) three position coaxial switch 140 toselectively connect the output of network 112 to either electrode 16 orelectrode 34 or to neither electrode 16 or electrode 34, and (2) threeposition coaxial switch 142 to selectively connect the output ofmatching network 114 to either electrode 36 or electrode 42 or toneither electrode 36 or electrode 42. Controller 24, in conjunction withactivation of switches 116 and 142, activates switches 69, 72 and 110 toprevent any of electrodes 16, 34, 36 or 42 which are connected to theoutput terminals of networks 112 and 114 from being grounded, asdescribed supra in connection with the circuitry associated with source54.

Controller 24 activates the various switches of FIG. 2 to provide greatversatility to the various combinations and permutations of the severalfrequencies that can be applied to electrodes 16, 34, 36 and 42. Forexample, the low, medium and high frequencies of sources 52, 54 and 56can be simultaneously applied to electrode 16 while switches 69, 71 and110 are closed to ground electrodes 34, 36 and 42. Under thesecircumstances, different portions of the energy at each of thefrequencies of sources 52, 54 and 56 is shunted to ground in plasmaconfinement region 8, as a result of electric field coupling fromelectrode 16 to the ground potential of electrodes 34, 36 and 42. Theamount of energy at each of frequencies F1, F2 and F3 coupled fromelectrode 16 to the ground potential of electrodes 34, 36 and 42 is afunction of (1) the wavelength associated with each of the threefrequencies, (2) the distance between electrodes 16 and 36, (3) thedistance between electrodes 16 and 34, and (4) the distance betweenelectrodes 36 and 42. The distances between the various combinations ofelectrodes in chamber 10 are controlled by the geometry of theelectrodes and by motor 47, inter alia.

A second exemplary situation involves applying the low and mediumfrequencies to bottom electrode 16, while applying the high frequency totop electrode 36, while grounding electrodes 34 and 42 and closingswitch 65 so a low impedance path is provided through bandpass filter 67for only the low frequency from electrode 36 to ground. In addition,switches 96 and 142 are activated to connect electrode 36 to the outputterminal of network 78 and the input terminal of network 78 to groundthrough resistor 100, resulting in a low impedance path to groundthrough network 78 from electrode 36 for the mid-frequency of source 54.Because of the high frequency of source 56 and relatively close spacingbetween electrodes 36 and 42, the electric field at the high frequencyhas a tendency to remain primarily in the upper portion of region 8 toprovide a relatively large electric field density for dissociationpurposes to the gas flowing from source 37 into region 8. The electricfield at the high frequency does not have a tendency to be coupled toelectrode 16 because there is no low impedance path at the highfrequency from electrode 16 to ground. Networks 58 and 76 areeffectively bandpass filters for the low and medium frequencies thatreject current at the high frequency. Because networks 58 and 76 have ahigh impedance to the high frequency, networks 58 and 76 decouple thehigh frequency from electrode 16.

In contrast to the electric field associated with high frequency F3, theelectric field associated with the low frequency F1 of source 52 extendsfrom electrode 16 to (1) electrode 34, (2) electrode 36 and (3)electrode 42. The resulting current at frequency F1 in electrode 36flows through the low impedance path of filter 67 to ground.Consequently, the electric field associated with frequency F1 affectsion energy throughout region 8.

The electric field associated with medium frequency F2 of source 54extends primarily from electrode 16 to electrode 34, as well as toelectrode 36, and to a lesser extent to electrode 42. The resultingcurrent at frequency F2 in electrode 36 flows through the low impedancepath of network 78 to ground via switches 108 and 96 and resistor 100.

A third exemplary situation involves applying the low and mediumfrequencies to bottom electrode 16 and the medium frequency to topelectrode 36 while grounding electrodes 34 and 42 and closing switch 65so a low impedance path is provided for only the low frequency fromelectrode 36 to ground through bandpass filter 67. Thereby, the lowfrequency of source 52 is coupled to the plasma in region 8 in the samemanner as described supra for the second exemplary situation. The highfrequency of source 56 is not a factor for the third exemplary situationbecause controller 24 causes switches 140 and 142 to engage the opencircuited terminals thereof. The medium frequency of source 54 iscoupled to electrodes 16 and 36 by virtue of switch 74 engaging itsthird output terminal so that splitter 80 is responsive to power fromsource 54. Controller 24 activates switches 106 and 108 so that theoutputs of networks 76 and 78 respectively drive electrodes 16 and 36.Consequently, electric fields at the medium frequency are coupledbetween (1) electrodes 16 and 36, (2) electrodes 16 and 34, and (3)electrodes 36 and 42. As a result, electric fields at the mediumfrequency affect ion energy, plasma density and molecular dissociationthroughout region 8.

A fourth exemplary situation involves applying the low frequency toelectrode 16 and the medium and high frequencies to electrode 36, whileelectrodes 34 and 42 are grounded. In this situation, controller 24activates (1) switches 74 and 116 to the second positions thereof, (2)switches 108 and 142 so the output terminals of network 78 and 114 areconnected to electrode 36, (3) switches 94 and 96 so the input terminalsof network 78 are connected to sensor 92, (4) switches 128 and 130 sothe input terminals of network 114 are connected to sensor 126, (5)switches 106 and 140 so the output terminals of networks 76 and 112 arerespectively connected to electrode 16 and open circuited, and (6)switches 86 and 124 so the input terminals of networks 76 and 112 areconnected to ground through resistors 90 and 132, respectively.Consequently, the low frequency of sources 52 has a low impedance pathfrom electrode 36 to ground through bandpass filter 67, but thefrequencies of sources 54 and 56 do not have such low impedance pathsfrom electrode 36 to ground. As a result, the low frequency of source 52is coupled to the plasma in region 8 in the same manner as describedsupra for the second exemplary situation. Low impedance paths exist fromthe output terminals of network 78 through switch 108 to electrode 36,thence through the plasma in region 8 to (1) electrode 16 to groundthrough network 76, switch 86 and resistor 98 and (2) electrode 42 toground. Consequently, substantial electric fields at the mediumfrequency are in region 8 between electrodes 36 and 42, as well asbetween electrodes 16 and 36. As a result, there is primary control ofion distribution in the upper portion of region 8, as well as across thecenter portion of region 8 between electrodes 16 and 36. The only lowimpedance path for the high frequency of source 56 for this situation isbetween electrodes 36 and 42. There is no low impedance path betweenelectrodes 16 and 36 for the high frequency of source 56 becauseelectrode 16 is decoupled from the output terminals of network 112 byvirtue of switch 140 being open circuited. The spacing betweenelectrodes 36 and 34 for the high frequency of source 56 is such thatthe impedance for the high frequency through the plasma betweenelectrodes 34 and 36 is substantially greater than the impedance betweenelectrodes 36 and 42. Consequently, the high frequency of source 56affects the plasma in region 8 in the same manner as described supra forthe second exemplary situation.

In a fifth exemplary situation, the low and medium frequencies ofsources 52 and 54 are applied to bottom electrode 16, while each ofelectrodes 34, 36 and 42 is grounded. To this end, controller 24activates switch 106 to connect the output of network 76 to electrode16, while closing each of switches and 69, 71 and 110. The plasma inregion 8 is thereby affected by the low and medium frequencies ofsources 52 and 54 in the same way as described for the low and mediumfrequencies for the first exemplary situation. The plasma in region 8 isnot affected by the high frequency of source 56 for the same reasons setforth in the third exemplary situation.

In other exemplary situations, controller 24 can control the variousswitches of FIG. 2 so only the low frequency of source 52 is connectedto electrode 16 and neither source 54 nor source 56 is connected to anyof the electrodes. In such a situation, controller 24 closes switch 110and chamber 10 processes the workpiece in a somewhat primitive manner.Alternatively, controller 24 can connect the output of either or both ofsources 54 and 56 to any of electrodes 16, 34, 36 or 42. For example, itmay be desirable to couple the high frequency of source 56 betweenelectrodes 16 and 36, while coupling the medium frequency of source 54between electrodes 36 and 34. In such a situation, controller 24 (1)opens switches 69, 71, 72 and 110, (2) activates switches 74, 94 and 96and switches 116, 128 and 130 so the outputs of sources 54 and 56 arerespectively applied to input terminals of networks 78 and 114, (3)activates switches 108 and 142 so the outputs of networks 78 and 114 areconnected to electrode 36, (4) activates switches 106 and 86 so there isa low impedance path from electrode 34 to ground through network 76 andresistor 94 for the medium frequency of source 54, and (5) activatesswitches 140 and 124 so there is a low impedance path from electrode 16to ground through network 112 and resistor 132 for the high frequency ofsource 56. Consequently, electric fields are established in region 8 for(1) only the high frequency of source 56 between electrodes 16 and 36and (2) only the medium frequency of source 54 between electrodes 34 and36. Because there is no low impedance path to ground from electrode 16for the medium frequency of source 54 there is no substantial electricfield established in region 8 between electrodes 16 and 36 for themedium frequency. Because there is no low impedance path to ground fromelectrode 34 for the high frequency of source 56, there is nosubstantial electric field for the high frequency established in region8 between electrodes 34 and 36. It is also to be understood thatsuitable bandpass filter circuitry similar to that described andillustrated can be employed for providing a low impedance path betweenelectrodes 36 and 42 only for the high frequency of source 56.

Reference is now made to FIG. 3 of the drawing, a schematic diagram of asecond embodiment of chamber 10. The embodiment of FIG. 3 is similar tothe embodiment of FIG. 1, but the embodiment of FIG. 3 has a much largervolume plasma confinement region that extends to chamber wall 12 andbase 19. Consequently, the embodiment of FIG. 3 does not include louvers44 and the pressure of the plasma processing workpiece 18 is controlledexclusively by using pressure control for vacuum pump 9. The entirebottom face of metal ring 40, the side wall of ring 32 and the interiorsurface of side wall 12 are all grounded and define parts of theboundary of the plasma confinement region in the embodiment of FIG. 3.To prevent chemical contamination by the plasma of any of the bottomface of metal ring 40, the side wall of ring 32 or the interior surfaceof side wall 12, all of these surfaces are covered with plates 100 madeof an electrically conductive or dielectric material, such as intrinsicsilicon, that does not contaminate the chemistry of the plasma in region8. Because side wall 12 is part of the plasma confinement region in theembodiment of FIG. 3, the temperature of the side wall is controlled ina manner similar to that described for control of electrode assembly 14in the embodiment of FIG. 1.

The electrodes in the embodiment of FIG. 3 are responsive to several RFfrequencies and controlled as described supra in connection with FIGS. 1and 2. The electric fields in the chamber of FIG. 3 differ considerablyfrom the electric fields in the chamber of FIG. 1 because of the largevolume and complex shape of the plasma confinement region in the FIG. 3embodiment. However, the electric field effects on the plasma aresomewhat similar in the embodiment of FIG. 3 to those described inconnection with the embodiment of FIGS. 1 and 2.

FIGS. 9A and 9B illustrate a computer system 800, which is suitable forimplementing a controller 24 used in embodiments of the presentinvention. FIG. 9A shows one possible physical form of the computersystem. Of course, the computer system may have many physical formsranging from an integrated circuit, a printed circuit board, and a smallhandheld device up to a huge super computer. Computer system 800includes a monitor 802, a display 804, a housing 806, a disk drive 808,a keyboard 810, and a mouse 812. Disk 814 is a computer-readable mediumused to transfer data to and from computer system 800.

FIG. 9B is an example of a block diagram for computer system 800.Attached to system bus 820 is a wide variety of subsystems. Processor(s)822 (also referred to as central processing units or CPUs) are coupledto storage devices, including memory 824. Memory 824 includes randomaccess memory (RAM) and read-only memory (ROM). As is well known in theart, ROM acts to transfer data and instructions uni-directionally to theCPU and RAM is used typically to transfer data and instructions in abi-directional manner. Both of these types of memories may include anysuitable of the computer-readable media described below. A fixed disk826 is also coupled bi-directionally to CPU 822; it provides additionaldata storage capacity and may also include any of the computer-readablemedia described below. Fixed disk 826 may be used to store programs,data, and the like and is typically a secondary storage medium (such asa hard disk) that is slower than primary storage. It will be appreciatedthat the information retained within fixed disk 826 may, in appropriatecases, be incorporated in standard fashion as virtual memory in memory824. Removable disk 814 may take the form of any of thecomputer-readable media described below.

CPU 822 is also coupled to a variety of input/output devices, such asdisplay 804, keyboard 810, mouse 812 and speakers 830. In general, aninput/output device may be any of: video displays, track balls, mice,keyboards, microphones, touch-sensitive displays, transducer cardreaders, magnetic or paper tape readers, tablets, styluses, voice orhandwriting recognizers, biometrics readers, or other computers. CPU 822optionally may be coupled to another computer or telecommunicationsnetwork using network interface 840. With such a network interface, itis contemplated that the CPU might receive information from the network,or might output information to the network in the course of performingthe above-described method steps. Furthermore, method embodiments of thepresent invention may execute solely upon CPU 822 or may execute over anetwork such as the Internet in conjunction with a remote CPU thatshares a portion of the processing.

In addition, embodiments of the present invention further relate tocomputer storage products with a computer-readable medium that havecomputer code thereon for performing various computer-implementedoperations. The media and computer code may be those specially designedand constructed for the purposes of the present invention, or they maybe of the kind well known and available to those having skill in thecomputer software arts. Examples of computer-readable media include, butare not limited to: magnetic media such as hard disks, floppy disks, andmagnetic tape; optical media such as CD-ROMs and holographic devices;magneto-optical media such as floptical disks; and hardware devices thatare specially configured to store and execute program code, such asapplication-specific integrated circuits (ASICs), programmable logicdevices (PLDs) and ROM and RAM devices. Examples of computer codeinclude machine code, such as produced by a compiler, and filescontaining higher level code that are executed by a computer using aninterpreter. Computer readable media may also be computer codetransmitted by a computer data signal embodied in a carrier wave andrepresenting a sequence of instructions that are executable by aprocessor.

FIG. 4 is a high level flow chart of a process used in an embodiment ofthe invention. A substrate with an etch layer and a mask over the etchlayer is placed in a process chamber (step 404). The process chamber maybe either chamber as illustrated in FIG. 1 and FIG. 3, which is able toprovide RF power at at least three different frequencies simultaneously.FIG. 5A is a schematic cross-sectional view of a substrate 504 with alayer 508 that has to be etched over which a mask 512 has been placed.The mask material that has to be etched can be either photoresist ofvarious types (e.g. DUV, 193 nm or 157 nm) or different hardmaskmaterials (e.g. poly-silicon, Titanium Nitride etc.)

An etchant gas is provided to the process chamber (step 408). Theetchant gas may be a conventional etchant gas. A first etch step isprovided with a first frequency, a second frequency different from thefirst frequency, and a third frequency different from the first andsecond frequencies, where the first etch etches a feature in thedielectric layer to a first depth (step 412). FIG. 5B is a schematiccross-sectional view of the substrate 504 with the etch layer 508, aftera feature 516 has been etched in the etch layer 508 to a first depth520. The power settings for the RF sources are optimized to etch to thefirst depth producing the aspect ratio of the feature width to thefeature depth. In an example, the first frequency is at a first power,the second frequency is at a second power, and the third frequency is ata third power, where the at least the first power and the third powerare greater than zero and where the first etch etches a feature in thedielectric layer to a first depth.

A second etch step is provided at a different power than the first step,where the second etch etches the feature in the dielectric layer to asecond depth greater than the first depth (step 416). FIG. 5C is aschematic cross-sectional view of the substrate 504 with the etch layer508, after the feature 516 has been etched in the etch layer 508 to asecond depth 524 deeper than the first depth. The power settings for theRF sources are optimized to etch from the first depth to the seconddepth producing the aspect ratio of the feature width to the featuredepth. To continue with the above example, the first frequency is at afourth power level, the second frequency is at a fifth power level, andthe third frequency is at a sixth power level, where at least one of thefourth and sixth powers is greater than zero and the fifth power isgreater than zero and where a condition is selected from the group ofthe first power not being equal to the fourth power and the third powernot being equal to the sixth power, wherein the second etch etches thefeature in the dielectric layer to a second depth greater than the firstdepth.

A third etch step is provided at a different power than the second,where the third etch etches the feature in the dielectric layer to athird depth greater than the second depth (step 416). FIG. 5D is aschematic cross-sectional view of the substrate 504 with the etch layer508, after the feature 516 has been etched in the etch layer 508 to athird depth 528 deeper than the second depth. The power settings for theRF sources are optimized to etch from the second depth to the thirddepth producing the required aspect ratio of the feature width to thefeature depth. To continue the above example, the first frequency is ata seventh power level, the second frequency is at a eighth power level,and the third frequency is at a ninth power level, where at least two ofthe seventh, eighth, and ninth powers are greater than zero and where acondition is selected from the group of the seventh power not beingequal to the fourth power, the eighth power not being equal to the fifthpower, and the ninth power not being equal to the sixth power, whereinthe third etch etches the feature in the dielectric layer to a thirddepth greater than the second depth. The high aspect ratio contactetching is not necessarily limited to only 3 steps. As the control ofthe HAR etch is required, more or less number of steps can be used inorder to control the profile along the etch process.

For high aspect ratio contacts HARC, as a contact is etched deeper,etching mechanisms change. For example, as the etch depth increases, theetch rate decreases. In addition, bowing may increase and etchselectivity to the mask may decrease. The use of at least threefrequencies and changing the power of these frequencies as the etchproceeds allows for the resulting plasma to be tailored to the etchdepth and required profile providing an improved, optimized etch. Thismay be done by using different RF powers of various frequencies, usingthe same etch reactants mixture. Usually, in order to control theprofile along the etch, different etch reactant mixtures are used. Thereason for this approach is mainly because they provide differentspecies in the plasma. Instead, in this invention, control ofspeciations in the plasma is by using RF powers of various frequencies.

FIGS. 6A-C summarize the etch profile at a specific time during the etchand the power conditions (presented in the preceding paragraphs)required for every step. This schematic refers to a 3 step etch processwhere d1 is the etch depth after the step S1 (shown in FIG. 6A), d2 isthe etch depth after the step S2 (shown in FIG. 6B), d3 is the etchdepth after the step S3 (Shown in FIG. 6C). P1 to P9 are the notationsfor the power level used and F1, F2, F3 are the used frequencies.

Table 1 summarizes the power conditions required for each of the threesteps.

TABLE 1 Step 1 Step 2 Step 3 Condi- F1_at power_P1 F4_at power_P4 F7_atpower_P7 tions F2_at power_P2 F5_at power_P5 F8_at power_P8 F3_atpower_P3 F6_at power_P6 F9_at power_P9 (P1 > 0 and P3 > 0) P4 ≠ P1 or P6≠ P3 P7 ≠ P4 or P8 ≠ P5 or or P5 ≠ P1 or P9 ≠ P6 (P1 > 0 and P2 > 0)(P4 > 0 and (P5 > 0 (P7 > 0 and P8 > 0) or P6 > 0)) or or (P7 > 0 andP9 > 0) (P4 > 0 and (P5 > 0 or and P6 > 0)) (P8 > 0 and P9 > 0) or (P7 >0 and P8 > 0 and P9 > 0)

For step S1, shown in FIG. 6A, frequency F1 is set to power level P1,frequency F2 is set to power level P2, and frequency F3 is set to powerlevel P3. (P1>0 and P3>0) or (P1>0 and P2>0).

For S2, shown in FIG. 6B, frequency F1 is set to power level P4,frequency F2 is set to power level P5, and frequency F3 is set to powerlevel P6. P4≠P1 or P6≠P3 or P5≠P1. (P4>0 and (P5>0 or P6>0)) or (P4>0and (P5>0 and P6>0)).

For S3, shown in FIG. 6C, frequency F1 is set to power level P7,frequency F2 is set to power level P8, and frequency F3 is set to powerlevel P9. P7≠P4 or P8≠P5 or P9≠P6. (P7>0 and P8>0) or (P7>0 and P9>0) or(P8>0 and P9>0) or (P7>0 and P8>0 and P9>0).

This case is particularized for simplicity, but combinations orpermutations of these steps can be possible (e.g. have step S2 insteadof S3, and S3 instead of S2, OR even have S3 excluded). Also, dependingof the difficulty of the etch, more etch steps can be added in order toperform the full etch process. Also alternating between etch steps ispossible (e.g. run S2 followed by S3, each of them for shorter timeperiods, and followed subsequently by the runs S2 and S3 again).

Preferably, the first frequency is in the range from 100 kHz to 10 MHz.More preferably, the first frequency is about 2 MHz. Preferably, thesecond frequency is in the range from 10 MHz to 35 MHz. More preferably,the second frequency is about 27 MHz. Preferably, the third frequency isgreater than 40 MHz. More preferably, the third frequency is about 60MHz.

The speciation for the same etch chemistry mixture and the same powerlevel is represented in FIG. 7. The ion flux of each particular ion wasnormalized to unity for each particular frequency. A first curve 604shows the fraction of total ion flux for CF₃ ⁺ at various frequencies. Asecond curve 608 shows the fraction of total ion flux for C₂F₄ ⁺ atvarious frequencies. A third curve 612 shows the fraction of total ionflux for CF⁺ at various frequencies. A fourth curve 616 shows thefraction of total ion flux for C₃F₅ ⁺ at various frequencies. A fifthcurve 620 shows the fraction of total ion flux for Ar⁺ at variousfrequencies. A sixth curve 624 shows the fraction of total ion flux forCHF₂ ⁺ at various frequencies. A seventh curve 628 shows the fraction oftotal ion flux for C₂F₅ ⁺ at various frequencies. This graph illustrateshow various frequencies influence the fraction of speciation. Therefore,the speciation in the plasma can be controlled by varying the RFfrequency along the etch process.

FIG. 8A shows the variation of the ion energy and distribution as afunction of RF power for the same frequency (27 MHz). The ion energydistribution of one of the main ions in a hydrofluorocarbon plasma: CHF₂⁺ (having a mass of 51 atomic units) is represented here. The curve 704shows ion energy and distribution for the ion CHF₂ ⁺ when only a 27 MHzsignal is supplied to the plasma at the power level of 200 W. The curve708 shows ion energy and distribution for the ion CHF₂ ⁺, when the 27MHz signal is supplied at 400 Watts. The third curve 712 shows ionenergy and distribution for the ion CHF₂ ⁺, when the 27 MHz signal issupplied at 800 Watts. The fourth curve 716 shows ion energy anddistribution for the ion CHF₂ ⁺, when the 27 MHz signal is supplied at1200 Watts. The fifth curve 720 shows ion energy and distribution forthe ion CHF₂ ⁺, when 27 MHz signal is supplied at 1600 Watts. The sixthcurve 724 shows ion energy and distribution for the ion CHF₂ ⁺, when the27 MHz signal is supplied at 2000 Watts.

By comparison, FIG. 8B shows the variation of the ion energy anddistribution of the same ion CHF₂ ⁺ as a function of RF power for thesame, higher frequency (60 MHz). The curve 744 shows ion energy anddistribution for the ion CHF₂ ⁺, when only 60 MHz signal is supplied tothe plasma at the power level of 100 W. The curve 748 shows ion energyand distribution for the ion CHF₂ ⁺, ion when 60 MHz signal is suppliedat 200 Watts. The third curve 752 shows ion energy and distribution forthe ion CHF₂ ⁺, when the 60 MHz signal is supplied at 400 Watts. Thefourth curve 756 shows ion energy and distribution for the ion CHF₂ ⁺,when the 60 MHz signal is supplied at 800 Watts. The fifth curve 760shows ion energy and distribution for the ion CHF₂ ⁺, when 60 MHz signalis supplied at 1100 Watts.

By comparing FIG. 8A and FIG. 8B, it is clear that specific ion energylevels (e.g. as low as 80 W) cannot be obtained with a specific RFfrequency (e.g. 27 MHz), but they are accessible with the higher RFfrequency (e.g. 60 MHz). Concluding, by varying the RF frequency and thepower levels, not just the speciation in the plasma can be modified butalso the ion energy and its distribution.

In the etching of a high aspect ratio feature, as the etch progresses,the invention optimizes different etching conditions (e.g. ion toneutrals ratio, ion energy distribution) along the etch. At thebeginning of the HAR contact etching less aggressive etching conditionsmay be used. That will ensure a good PR selectivity, less PR facetingand as a consequence less bowing. This can be accomplished by usingpreferentially the higher frequency power (e.g. 60 MHz or even higher,)and having relative lower power levels for the lower frequencies (e.g.27 and 2 MHz). Bow creation may be further avoided by using this etchuntil the etching passes the bow level. As the aspect ratio increasesthe ions to neutral ratio decreases and also a more pronounced ionenergy dependence is expected to be seen. Therefore more higher energyions are required to be able to continue the etch. This can beaccomplished by using preferentially 27 and 2 MHz at different powerlevels toward the end of the etch process. This may be accomplished byincreasing power from the 27 and/or 2 MHz RF sources and possiblydecreasing the power from the 60 MHz power source. Increasing the powerfrom the 27 MH RF source may also increase mask selectivity, which isvery helpful when high aspect ratio contacts are to be etched.

It has been further found that to reduce bowing the right amount ofselectivity is needed. Too much or too little selectivity may increasebowing.

An etchant gas that may be used in embodiments of the invention may havea fluorocarbon or hydrofluorocarbon component. An inert gas such asargon and/or xenon and/or any other inert gas may be added as acomponent of the etchant gas. Oxygen may be another component of theetchant gas.

Preferably, the layer to be etched is a dielectric layer. Morepreferably, the layer to be etched is a silicon oxide layer. Preferably,the layer to be etched is a single layer. More preferably, the layer tobe etched is a single uniform layer.

EXAMPLE Example 1 In this Example a Contact is Etched in Oxide using aBasic C₄F₈ Chemistry

The etch used an etch gas of 250 sccm Ar, 28 sccm C₄F₈, and 10 sccm ofO₂, which is flowed into the chamber. Chamber pressure is set to 50mTorr. A first RF power source provides a first RF signal of 2 MHzfrequency. A second power source provides a second RF signal of 27 MHzfrequency. A third power source provides a third RF signal of 60 MHzfrequency.

In a first etch step the first power source provides 2000 Watts at 2MHz, the second power source provides 0 Watts at 27 MHz, and the thirdpower source provides 1000 Watts at 60 MHz. This step is provided for120 seconds.

In a second etch step, the first power source provides 1400 Watts at 2MHz, the second power source provides 1400 Watts at 27 MHz, and thethird power source provides 200 Watts at 60 MHz. This step is providedfor 120 seconds.

The resulting feature has a depth of 3.0 μm and a top CD of 0.18 μm:Therefore, the aspect ratio of the feature is 3.0/0.18, which isapproximately 16.7.

Example 2 In this Example a Contact is Etched in Oxide using a BasicC₄F₆ Chemistry

The etch used an etch gas of 400 sccm Ar, 30 sccm C₄F₆, and 24 sccm ofO₂, which is flowed into the chamber. Chamber pressure is set to 35mTorr. A first RF power source provides a first RF signal of 2 MHzfrequency. A second power source provides a second RF signal of 27 MHzfrequency. A third power source provides a third RF signal of 60 MHzfrequency.

In a first etch step, the first power source provides 2000 Watts at 2MHz, the second power source provides 200 Watts at 27 MHz, and the thirdpower source provides 1000 Watts at 60 MHz. This step is provided for100 seconds.

In a second etch step, the first power source provides 2000 Watts at 2MHz, the second power source provides 600 Watts at 27 MHz, and the thirdpower source provides 600 Watts at 60 MHz. This step is provided for 100seconds.

In a third etch step, the first power source provides 1400 Watts at 2MHz, the second power source provides 1500 Watts at 27 MHz, and thethird power source provides 100 Watts at 60 MHz. This step is providedfor 80 seconds.

The resulting feature has a depth of 2.6 μm and a top CD of 0.16 μm:Therefore, the aspect ratio of the feature is 2.6/0.16, which is 16.25.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, modifications andvarious substitute equivalents, which fall within the scope of thisinvention. It should also be noted that there are many alternative waysof implementing the methods and apparatuses of the present invention. Itis therefore intended that the following appended claims be interpretedas including all such alterations, permutations, modifications, andvarious substitute equivalents as fall within the true spirit and scopeof the present invention.

1. An apparatus for etching a feature in an etch layer through a maskover a substrate, comprising: a plasma processing chamber, comprising: achamber wall forming a plasma processing chamber enclosure; a substratesupport for supporting a substrate within the plasma processing chamberenclosure; a pressure regulator for regulating the pressure in theplasma processing chamber enclosure; at least one electrode forproviding power to the plasma processing chamber enclosure forsustaining a plasma; a gas inlet for providing gas into the plasmaprocessing chamber enclosure; and a gas outlet for exhausting gas fromthe plasma processing chamber enclosure; a gas source in fluidconnection with the gas inlet; a first power source for providing powerwithin the chamber wall at a first frequency; a second power source forproviding power within the chamber wall at a second frequency differentthan the first frequency; a third power source for providing powerwithin the chamber wall at a third frequency different than the firstfrequency and the second frequency; and a controller controllablyconnected to the gas inlet, the first power source, the second powersource, and the third power source, comprising: at least one processor;and computer readable media, comprising: computer readable code forintroducing an etchant gas through the gas inlet; computer readable codefor performing a first etch step, comprising: providing energy from thefirst power source at a first power level; providing energy from thesecond power source at a second power level; providing energy from thethird power source at a third power level, wherein in the first powerlevel and the third power level are greater than zero, wherein the firstetch is used to etch a feature in the layer to be etched to a firstdepth; and computer readable code for performing a second etch step,comprising: providing energy from the first power source at a fourthpower level; providing energy from the second power source at a fifthpower level; providing energy from the third power source at a sixthpower level, wherein at least one of the fourth and sixth power levelsis greater than zero and the fifth power level is greater than zero, andwherein a condition is selected from the group of the first power levelnot being equal to the fourth power level and the third power level notbeing equal to the sixth power level, wherein the second etch etches thefeature in the layer to be etched to a second depth greater than thefirst depth.
 2. The apparatus, as recited in claim 1, wherein the firstfrequency is between 100 kHz and 10 MHz, the second frequency is between10 MHz to about 35 MHz, and the third frequency is greater than 40 MHz.3. The apparatus, as recited in claim 2, wherein the layer to be etchedis a dielectric layer.
 4. The apparatus, as recited in claim 3, whereinthe dielectric layer is a single layer.
 5. The apparatus, as recited inclaim 2, wherein the single layer is a uniform layer.
 6. The apparatus,as recited in claim 2, further comprising a third etch step, wherein atleast two of the seventh, eighth, and ninth powers is greater than zeroand where a condition is selected from the group of the seventh powernot being equal to the fourth power, the eighth power not being equal tothe fifth power, and the ninth power not being equal to the sixth power,wherein the third etch etches the feature in the dielectric layer to athird depth greater than the second depth.
 7. The apparatus, as recitedin claim 6, wherein the first frequency is about 2 MHz, the secondfrequency is about 27 MHz, and the third frequency is about 60 MHz. 8.The apparatus, as recited in claim 1, wherein the etchant gas comprisesa component gas selected from the group of a fluorocarbon and ahydrofluorocarbon.
 9. The apparatus, as recited in claim 1, furthercomprising a third etch step, wherein at least two of the seventh,eighth, and ninth powers is greater than zero and where a condition isselected from the group of the seventh power not being equal to thefourth power, the eighth power not being equal to the fifth power, andthe ninth power not being equal to the sixth power, wherein the thirdetch etches the feature in the dielectric layer to a third depth greaterthan the second depth.
 10. The apparatus, as recited in claim 9, whereinthe first frequency is about 2 MHz, the second frequency is about 27MHz, and the third frequency is about 60 MHz.
 11. An apparatus foretching a feature in an etch layer through a mask over a substrate,comprising: a plasma processing chamber, comprising: a chamber wallforming a plasma processing chamber enclosure; a substrate support forsupporting a substrate within the plasma processing chamber enclosure; apressure regulator for regulating the pressure in the plasma processingchamber enclosure; at least one electrode for providing power to theplasma processing chamber enclosure for sustaining a plasma; a gas inletfor providing gas into the plasma processing chamber enclosure; and agas outlet for exhausting gas from the plasma processing chamberenclosure; a gas source in fluid connection with the gas inlet; a firstpower source for providing power within the chamber wall at a firstfrequency; a second power source for providing power within the chamberwall at a second frequency different than the first frequency; a thirdpower source for providing power within the chamber wall at a thirdfrequency different than the first frequency and the second frequency;and a controller controllably connected to the gas inlet, the firstpower source, the second power source, and the third power source,comprising: at least one processor; and computer readable media,comprising: computer readable code for introducing an etchant gasthrough the gas inlet; computer readable code for performing a firstetch step using the first frequency, the second frequency, and the thirdfrequency to etch a feature into the etch layer to a first depth;computer readable code for performing a second etch step using the firstfrequency, the second frequency, and the third frequency, with at leastone of the frequencies at a different power level than that used in thefirst etch to etch the feature in the etch layer to a second depthgreater than the first depth; and computer readable code for performinga third etch step using the first frequency, the second frequency, andthe third frequency, with at least one of the frequencies at a differentpower level than that used in the second etch, to etch the feature intothe etch layer to a third depth greater than the second depth.
 12. Theapparatus, as recited in claim 11, wherein the layer to be etched is adielectric layer.
 13. The apparatus, as recited in claim 12, wherein thedielectric layer is a single layer.
 14. The apparatus, as recited inclaim 13, wherein the single layer is a uniform layer.
 15. Theapparatus, as recited in claim 11, wherein the first frequency isbetween 100 kHz and 10 MHz, the second frequency is between 10 MHz toabout 35 MHz, and the third frequency is greater than 40 MHz.
 16. Theapparatus, as recited in claim 11, wherein the first frequency is about2 MHz, the second frequency is about 27 MHz, and the third frequency isabout 60 MHz.